This proposal requests funds for the purchase of a matrix-assisted laser desorption time of flight mass spectrometer (MALD MS) for structural studies of bio-macromolecules and their constituents of importance to on- going research in biological and medical science in the San Francisco Bay Area. The shared instrument will be housed in the NIH/NSF supported Mass Spectrometry Facility at UCSF and enjoy the intellectual environment where many other complementary techniques are being applied to solve sequence and structural problems in protein and carbohydrate biology and medicine. The major users consist of the group of 16 scientists and clinicians involved in 12 NIH supported research programs. All projects involve research at the forefront of urgent biomedical problems concerning the identification of peptides, proteins, carbohydrates and covalent modifications of cellular macromolecules which will benefit from the unprecedented sensitivity of MALD for low molecular weight studies (less then or equal to 10,000 Da) and the unprecedented extended mass range (greater than 230,000 Da) for studies of intact biomacromolecules or their degradation products, e.g., human Apo B 100 modifications, etc. In addition, advantage will be taken of the power of this technique to explore new "crude" isolates in the presence of buffers necessary to preserve biological activity. Problems range from the identification of antigenic peptides presented by Class I and II histocompatibility molecules, discovery of new proteins induced by cytokines in melanoma cells, to rational drug design, membrane bound receptors, fundamental studies of receptor mediated uptake of circulating proteins and glycoproteins, and bacterial antigens. The internal Advisory Committee will be responsible for the overall guidance of the instrument's shared use for cost-effective provision of this revolutionary new mass spectrometric information for the group of users. Up to 20% of the instrument time will be available for projects originating outside the major user group with the consultation of the Advisory Committee. UCSF School of Pharmacy has guaranteed $38,280 for a full service contract for the second year operation after warranty. Long term operation and maintenance will be assured by the association with a major Mass Spectrometry Facility and support from the major users.